Multiple lines of evidence implicate dysfunction of forebrain interneurons in the symptomatology of major neuropsychiatric illnesses, including schizophrenia, autism, and epilepsy. This dysfunction involves subtypes of interneurons that differ in their neurochemistry, connectivity, and physiology. Unfortunately, gaining a detailed molecular and cellular grasp of how alterations of interneuron-related disease genes actually affect interneuron development or function has been exceedingly difficult. This is due, in part, to our general inability to obtain biopsy-like brain specimens from diseased individuals for in vitro studies. Recently, advances in the derivation of neurons from mouse and human stem cells suggest that pluripotent cells can be used to study developmental neurogenetics and function. My lab and others have begun to make progress in deriving cortical interneurons from mouse and human stem cells. In particular, we can generate cells that express molecular markers of interneuron progenitors of the basal forebrain of both mouse and human, and we can show that these cells can migrate and survive extensively after transplantation into mouse cortex, express GABA and other interneuron markers and, in the case of mouse ES derived interneurons, have interneuron subtype-like physiological characteristics. However, major hurdles must be solved before the stem cell system is ready for broad usage in the search for causes and treatments of interneuron-related disorders. For example, since distinct interneuron subtypes are differentially affected in various disorders, how will we generate these subtypes from human stem cells? Since key aspects of interneuron subtype function depend on specific patterns of inputs, intrinsic activity, and axonal targeting onto other neurons, what assays will allow us to study these features? Here we will use the experimentally facile mouse ES system to learn how to enrich stem cell differentiations for distinct subgroups or subtypes of cortical interneurons, and will apply that system to identify additional markers of fate-committed but highly immature interneuron precursors (Aim 1). We will then apply this information, together with results of ongoing studies, to generate interneuron subclasses from human stem cells (Aim 2). Aim 2 will involve both embryonic stem cells, that have the advantage of being better characterized and are not affected by the genetic disruptions associated with induced pluripotent stem cell (IPSC) reprogramming; and IPSCs, that are derivable from diseased individuals. In Aim 3 we will study loss of function effects of two disease-related genes on human interneuron migration and synaptogenesis. Success in this endeavor would enable a host of future studies on developmental and functional aspects of human interneurons, resulting in major advances in the etiology, prevention, and treatment of interneuron-related neuropsychiatric disease. PUBLIC HEALTH RELEVANCE: Dysfunction of forebrain interneurons is implicated in the causation of major neuropsychiatric illnesses, including schizophrenia, autism, and epilepsy. Unfortunately, gaining a molecular and cellular grasp of how alterations of interneuron-related disease genes actually affect the development or function of this neuronal subclass is limited by our lack of access to living, diseased, interneurons. This application proposes to bridge that gap by generating forebrain interneurons from human stem cells, and using this system to begin to examine how disease-related genes affect human interneuron development and function.